an uniform group or a uniform group? an office building or a office building?
"a uniform group"

"an office building"
The A/AN rule, which you should know, says that it depends on whether or not the word following A/AN STARTS with a vowel sound.

UNIFORM is pronounced "YOO-nih-form", which starts with a consonant sound, the "Y", which is pronounced as a consonant ("Yuh") not a vowel. So it's "A UNIFORM".

OFFICE starts with a vowel sound, so it's "AN OFFICE".
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I think the word "An" sounds better to me then "A"
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